1. Technical Field
Embodiments of the present invention relate generally to wireless digital communication technology, more specifically, to a system and method for reserving channels for high priority packets.
2. Description of the Related Art
A conventional wireless mesh network includes a plurality of nodes, each incorporating a digital radio transceiver. A given node may transmit payload data to one or more other nodes via the digital radio transceiver. The node may originate the payload data or forward the payload data on behalf of a different node. Similarly, a given node may receive the payload data from a different node to be processed or forwarded by the node. The wireless mesh network may include an arbitrary number of nodes and may include certain access points, configured to bridge data communications within the mesh network to a related service system, such as a wire line or optical communications network.
The digital radio transceiver may implement specific modulation and spectral utilization techniques to satisfy a particular set of technical requirements. For example, multi-channel frequency hopping spread spectrum (FHSS) may be implemented to avoid potentially excessive interference among nodes that are attempting to transmit on a common radio frequency channel in an arbitrary window of time. FHSS involves transmitting data on one radio frequency channel for up to a specified maximum time duration and subsequently transmitting on a different radio frequency channel for up to another specified maximum time duration. FHSS systems typically follow a specific channel hop sequence, which both the transmitter and receiver need to follow to maintain a reliable communications channel. The transmitter reduces average radio frequency energy associated with a given channel by hopping to a different channel after a specified maximum time duration, thereby reducing a probability of interference among nodes attempting to transmit on the same channel.
FHSS systems conventionally require the transmitter and receiver pair to be synchronized, which is typically accomplished via a synchronization procedure conducted between the transmitter and receiver. Overhead associated with the synchronization procedure and related transmission latencies can substantially reduce overall transmission efficiency and network throughput.
One challenge in implementing a wireless mesh network is achieving sufficient overall throughput and latency specifications. Overall throughput and latency are generally a function of overall utilization, link error rates, link bandwidth, and link transmission latency. As utilization increases, channel collision probabilities increase, leading to multiple dropped packets, which in turn result in additional overall utilization from transmission retry mechanisms. FHSS in wireless mesh networks offers certain benefits, including regulatory compliance in certain scenarios. However, inefficiencies associated with FHSS, such as transmission latency and synchronization overhead can significantly diminish overall network throughput and increase average link transmission latencies. In certain wireless mesh network applications, FHSS is required by prevailing regulations and overall network throughput and average latencies suffer from the above described inefficiencies.
Still another challenge in a FHSS wireless mesh environment is that high priority data may be handled in the same manner as other standard data. For example, in Aloha applications, standard priority transmissions are not distinguished from high-priority transmission.
Aloha has been used for packet radio environments where it is used with a particular Medium Access Control (MAC) protocol. As part of the MAC, every node is configured to hear every other node. Also, nodes that have data to transmit, begin their transmissions within predetermined slots. To address the issue that collisions in data transmission can occur, each node is able to detect a transmission failure. If a transmission failure occurs, the transmission is corrupted, but each transmitting node is able to detect the transmission failure. In response, each transmitting node re-transmits their respective data after waiting a random amount of time. In certain applications, the wait time is chosen according to a geometric statistical distribution that is independent from the number of transmissions. It is important that each of the transmitting nodes wait a different amount of time so as to avoid a transmission failure in the re-transmissions.
In an Aloha application, however, standard transmissions are not distinguished from high priority transmissions such that in a situation where a transmission failure occurs, a high priority message could wait a longer time for retransmission than would a standard priority message. In such a conventional implementation, the system (e.g., Aloha system) is not able to immediately address high priority messages that may be important for the integrity of the entire system or may be important from a business perspective.
As the foregoing illustrates, what is needed in the art is a more efficient technique for transmission in a wireless network environment.